i think i have a reasonable form of auto-complete working, for the scripting language in my mud:
whenever the parser signals an error, if it has a good idea of what it was expecting (keyword, symbol, in-scope variables, field & method names), it returns those as suggestions.
the text editor runs the parser as you type, and if the parser signals error suggestions around the cursor, the editor uses them for auto-complete.
i made a short demo video (below) which got "oooh"s from the two other players :)
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